The use of a continuously regenerated electrolytic membrane suppressor in ion analysis is well established. The primary function of a suppressor is to lower the background by converting chromatography eluent to a weakly dissociated form while converting fully dissociated sample analyte ions to a conductive form. Historically, there have been significant efforts dedicated to lowering the chromatographic noise of suppressor devices. The primary contributors of noise are a) suppressor background, b) leachate levels c) operational parameters such as current, temperature etc. These development efforts aided improved noise performance, particularly with eluents such as potassium hydroxide, sodium hydroxide, methanesulfonic acid etc. With eluents that were carbonate and/or bicarbonate based, the suppressed eluent was carbonic acid and resulted in higher noise relative to when the suppressed eluent was deionized water. One solution to the high noise issue has been to pass the suppressed eluent through a post suppressor carbonate removal device that removed the dissolved carbon dioxide from the carbonic acid effluent, thus lowering the background and achieving low noise.
Current-efficient electrolytic suppressors are described in U.S. Pat. No. 6,077,434 (the “'434 patent”). The structure of such suppressors may be a two-channel device with a sample stream flow channel separated from an ion receiving flow channel by an anion exchange barrier which passes eluent counterions to the analyte ions during suppression. Also, a three-channel sandwich-type suppressor is disclosed in which the sample stream flow channel is separated from flanking ion receiving channels by two ion exchange barriers. The upstream portion of the sample stream flow channel has lower electrical resistance than the downstream portion. The '434 patent discloses (at column 17, line 10 through column 18, line 7) a number of ways to accomplish this including the use of a first pair of electrodes for the upstream portion and another electrode pair for the downstream portion. Independent power sources for the electrode pairs or the use of a resistor in the downstream portion of the electrodes are disclosed as ways to lower the resistance in the downstream portion. At column 13, line 55 through column 14, line 11, the patent teaches that, if the sample stream flow channel is packed with ion exchange medium, it should be of low capacity.